In a situation where a new area is introduced that does not have a direct physical attachment to the backbone, a virtual link is used.
A virtual link provides a logical path between the ABR of the disconnected area and the ABR of the normal area that connects to the backbone. A virtual link must be established between two ABRs that have a common area, with one ABR connected to the backbone. Virtual Link Using Area 1 as a Transit Area illustrates a virtual link.
NoteVirtual links cannot be configured through a stub or NSSA area.
Virtual links are also used to repair a discontiguous backbone area. For example, in Virtual Link Providing Redundancy, if the connection between ABR1 and the backbone fails, the connection using ABR2 provides redundancy so that the discontiguous area can continue to communicate with the backbone using the virtual link.